Furnace



Jan. 13,1931.

J. L. M FARLA b FURNR? E Filed April 19, 1929 m e h. m 11 koF n .CC n M f ns H e m, W

' Patented Jan. 13,1931

UNITED STATES PATENT OFFICE JAMES L. MOFARLAND, OE SCHENECTADY, NEW YORK, ASSIGNOR TO GENERAL ELEC- TRIO COMPANY, A CORPORATION OF NEW YORK FURNACE Application filed April 19, 1929. Serial No. 856,534.

My invention relates to furnaces, more particularly to furnaces for brazing and annealing and the like, and has for its object the provision of a sim le, reliable and efficient method and means this character.

Although my invention is not limited thereto, it has particular application in the operation of furnaces for carrying out certain in heating operations for metals, such as brazing and annealing, in an atmosphere of a- Selected gas, such as hydrogen, which prevents oxidation of the metal during the heating 4 operation. One form of such a furnace is dis-' closed and claimed in the copending United States application of Carl L. Ipsen and-James L. McFarland. Serial No. 236,530, filed November 29, 1927, and assigned to the same assignee as this invention. a r

In the arrangement there described, the furnace chamber is filled with a selected gas,

preferably of hydro en content, through which the articles to e treated are passed. A portion of this chamber at the inlet end is 2 heated to a suitable high temperature to melt the brazing metal and form a'brazed joint while the remaining portion of the furnace constitutes a cooling chamber.

In order to produce uniform work and a maximum output, commensurate with the operating cost, it is desirable to use either pure hydrogen as the working medium or a gas-mixture comprising hydrogen in "fairly large proportions such as -80% by volume. In either case the gas medium will be explosive in character. By this it will be understood that if the gas medium is mixed with air and if this resultant gas mixture is heated or ignited a violent chemical action will take place accompanied bya flame and explosion. This action consists inthe sudden combination of the hydrogen and oxygen constituents of the mixture to form water. The temperature-to which the gas mixture must be heated to cause this chemical action iswell within the furnace operating temperature.

It will be appreciated, therefore, that it is very importantto prevent air from mixing with the furnace working gas medium, particularly when this gas is heated to the furor operating a furnace of form thereo nace working temperature. I have found, however, that in startin' a furnace of this character it is desirable, om the standpoint of economy both with respect to the as used and to the time re uired, to first heat the furnace, which is lled with air, substantially to its working temperature and then fill thefurnace with the working gas. Moreover, it is'desirable at times to cool the furnaceguickly so that it may be opened to the o uts1 e air as for example in case the operat1on ,of the furnace must be interrupted temporarily for internal repairs. To allow such a furnace to cool to a safe temperature at its natural rate requires from several days to a weeks time, the time required dependin upon the size of the furnace being coole Obviously this is an undesirable condition. 'In one of its aspects, my invention contemplates the provision of a simple, eflicient and safe method of filling the furnace with the working gas, irrespective of the furnace temperature, and moreover, for quickly cooling the highly heated furnace to a safe temperature at which it may be opened to the outside air. 7

In carryin my invention into effect in one I start up the furnace first by heating it substantially to its working temperature. In order to render'the furnace safe for the reception of either pure hydrogen or of a gas of hydrogen content, which is ex 10- sive in character, I introduce a gas whic is non-explosive in character, to expel the air from the furnace. This gas may be and preferably is a non-explosive mixture of hydrogen and nitrogen. However, nitro en alone may be used. After the furnace as been purged of the air I supply the furnace with the working as. In the eventit becomes necessa to coo the furnace rapidly so that it may opened to the outside air, I introduce a non-explosive gas as for example nitrogen, in sufficient quantities either to render the working gas non-explosive in character or to urge the furnace of the working gas. The

urnace may then be opened. To enhance the cooling operation, air ma be forced throu h the furnace. Of course t e air will be the line 3-3 of Fig. 1 looking in the direction of the arrows.

Referring to the drawing, I have shown my invention in one form in connection with an electric brazing furnace in which a hydrogen gas is selected for the working medium.

Preferably, the furnace will be of the form' described in the aforementioned copending application of Carl L. Ipsen and James L. McFarland. Briefl the constructionand operation of this urnace is as follows: As shown, the furnace comprises a cylindrical gas-tight steel shell orcasing 10 defining an elongated furnace chamber, this shell being supported in a horizontal and elevated position by means of a plurality of steel columns 11. Inside the shell at the inlet'end are top, bottom and side .walls 12 made of heat refractory bricks and defining a horizontal heating chamber 13 provided with relatively small inlet and outlet passages 13a and 13b. Suitable heating means, such as electrical heating resistors 15 (Fig. 2), is provided in the heating chamber 13, these resistors being hun on suitable heat refractory electrically insu ating projections or sup orts 16 built in the furnace wall. It will e understood that suitable terminals for the heating units are brought out for connection to a suitable electrical supply source through openings 17.

Inlet and outlet openings 18 and 19 respectively for the charge are provided in the bottom of the shell in opposite ends thereof. Access may be had to the interior of the shell for repairs, if necessary, through bulk heads 20 provided with removable covers.

The heating portion or chamber 13 and the connecting passages 13a and 13b occupy but a small portion of the total length of the furnace. The remaining portion of the furnace constitutes a cooling chamber, a' substantial portion of which is provided with a water jacket (Fig. 3) through which cooling water 22 is circulated. Suitable inlet and outlet openings 23 and 24 respectively for the water are provided in the bottom and top rtions of the furnace. 4 It will be understood that the articles to be heated are inserted into the heating chamber through the inlet opening 18 and move at a substantially uniform rate through the heating and cooling chambers to the opposite end where they are removed through the outlet opening 19.

Two series 25 and 26 (Figs. 2 and 3) of tracks extending through the chamber are provided'for the articles. The metal articles 27 to be brazed, shown as an assembly of parts with brazed material at the joints constituting a portion of an electric refrigeraare raised, a tray may be pushed from the elevator 35 into the heating chamber and at the same time a tray received from the cooling chamber onto the elevator 36. The trays are pushed through the furnace by means of a hydraulic motor 40 having a pusher piston 41 which extends through an opening in the inlet end of the furnace in position to engage the trays.

The openings 18 and 19 will be suitably sealed during the operation of the furnace so as to conserve the selected gas and thus the heat. Thus these openings will be only slightly larger than the trays and moreover will be normally closed by the elevators which ordinarily remain in their raised positions.

Preferably, also, the openings 18 and 19 are each provided with a pair of doors 43 which will be opened by the upward movement of the elevators and will be closed as the elevators are lowered. The heat will also be prei'.

It will be understood that in the operation of the furnace, the heating and cooling chambers will be maintained filled with the selected working gas medium which preferably will be admitted through a pipe 44'communicating with the top of the cooling chamber. 1

It'will be understood that the working gas will be supplied continuously to the furnace chamber. In order to insure that the furnace chamber pressure is at all times above atmospheric pressure andthusin order to insure that the working gas medium is being supplied continuously to the furnace in a quantity'and at a pressure suflicient to prevent the leakage of air into the furnace, the furnace will be provided with a small duct or tube 44a communicating with .the furnace chamber through which the working gas may escape. The gas escaping from this duct is ignited, combustion taking place at the outlet end of the tube. In the event the flame disappears, the attendant will be warned that the furnace pressure is below the desired value. The working gas supply will then be increased so as to bring the furnace pressure to the full working value.

7 As has been pointed out in starting up the furnace, it is desirable to fill the furnace with the working medium after the furnace has been heated substantially to its full operating temperature which is about 1100 C. In order to render the furnace safe for thereception of the working medium, I first purge the furnace of the air, which normally will be present by introducing a non-explosive gas into the furnace. Preferably this gas will be a non-explosive mixture of hydrogen and nitrogen. I

The purging mixture preferably will be admitted through a pipe 45 communicating with the furnace chamber at the bottom thereof while the air diluted with the purging gas will be allowed to escape through'the pipe 44. It will be understood, of course, that during this operation the pipe 44 will be disconnected from the source of working gas supply by suitable valve means (not shown) and open to the outside air to allow the escape of the air. Moreover, it will be understood, of course, that these pipe connections may be reversed. Thus the nonexplosive purging mixture may be admitted by means of the pipe 44 while the air mixture will be allowed toescape through the pipe 45. It may be desirable not to use a mixtureof nitrogen and hydrogen but to use pure nitrogen in the purging operation. The method of introduclng the purging gas in either'case will be the same.

When it is found that the gas escaping from the furnace is non-explosive in character, the furnace is safe for the reception of the working medium. It will be understood a that suitable gas tests will be made to determine the air content before the furnace will be supplied with the working medium. The gas may be tested conveniently by the ordinary test tube method. Thus the gas may be collected in a test tube and a flame be applied to the open end of the tube to determine whether or not the gas is inflammatory. If pure hydrogen be selected as the working gas medium the pure hydrogen will be admitted to the furnace in sufficient quantity to purge the furnace of the air purging gas. If a mixture of hydrogen and nitrogen be selected, the working gas may be supplied by either of two methods. Thus after the air purging operation, pure hydrogen may be admitted to bring the purging gas up to the full required hydrogen content. On the a other hand, it may be more convenient to introduce a previously prepared working mixture of the hydrogen and nitrogen. Thus the working mixture itself may be admitted in quantity suflicient to purge the furnace -sive in c be admitted either by the pipe 44 or by the pipe 45 it being understood that .suitable valve means (not shown) will be provided to control the sources of gas supply.

After the furnace has been supplied with the working gas, the trays carrying the articles to be heated will be pushed'through the furnace in end-to-end relation by means of the piston 41. It will be understood that the articles will be suitably inserted and removed from the furnace chamber by means of elevators 35 and 36. Preferably the motors provided to operate the elevators 35 and 36 and the pusher motor 40 will be suitably interlocked by means (not shown) to establish a predeterminedsequence of operation of the elevators and pusher mechanism.

In the event that it is necessary to cool the furnace quickly as for example in case the operation of the furnace must be temporarily interrupted for interior repairs, the working medium will be first driven out or rendered non-explosive in character. the working medium may be driven out by a non-explosive gas in a manner similar to the air purging process previously described, after which the furnace may be opened to the outside air and thus cooled rapidly, or the working medium may be rendered nonexplosive bythe introduction and mixture therewith with the furnace closed of a sufli cient quantity of the non-explosive gas after which the furnace may be opened. The nonexplosive gas may be a non-explosive mixture of hydrogen and nitrogen or pure nitrogen alone may be used for either of these operations. If the purging method is selected, the purging gas may be admitted through the pipe 45, while the working gas diluted with the purging gas will be allowed to escape through the top of the furnace by means of the pipe 44. When it is found that the gas escapinglthrough the pipe 44 is non-exploaracter, as determined by a suitable test, the furnace can'be opened and air admitted for rapid cooling. If desired, the purging gas may be admitted through the pipe 44 so as to force the working medium through the bottom opening.45. If it be desired to use the second method, i. e., if it be desired torender the working gas non-explosive in character before opening the furnace, the nitrogen gas or the nonexplosive mixture of hydrogen and nitrogen may be admitted through either the pipe 44 oi the pipe 45 with the furnace Thus chamber otherwise closed. Under these conditions it will be understood that a sufficient quantity of the non-explosive gas will be admitted to bring the furnace chamber 'filS within the non-explosive range, as determined by .a suitable'test, after which the furnace may be opened to the outside air.

To enhance the cooling operation, cooling air may be forced through the furnace chamher after it has been purged of the working gas or this gas has been rendered non-explosive in character. Thus the bulkheads 20 may be removed and the inlet and outlet openings 18 and 19 be opened so that air will be circulated through the furnace chamher by natural draft action. Or air may be forced through the furnace from one of its ends while the opening 18 or 19 at the opposite end will be opened to permit a free circulation of the air.

\Vhile I have in accordance with the pro visions of the patent statutes described my invention as embodied in concrete form and operating in a specific manner, it should be understood that I do not limit my invention thereto, since various modifications thereof will suggest themselves to those skilled in the art without departing from the spirit of my invention, the scope of which is set forth in the annexed claims.

What I claim as new and desire to secure by Letters Patent of the United States, is:

1. The method of operating a furnace wherein a working medium explosive in character is used in the furnace chamber which comprises heating said furnace chamber substantially to its operating temperature while filled with air, then admitting a non-explosive medium to purge the heated furnace chamber of air and thereafter supplying the furnace chamber with said working medium.

2. The method of operating a brazing furnace wherein a workmg gas of hydrogen content is used which comprises heating said 5. The method of quickly cooling a furnace wherein a working medium explosive gen gas is used which comprises forcing .nitrogen into the furnace chamber so as to purge the chamber of the explosive Working medium and thereafter admitting cooling air to the chamber. I

Injwitness whereof, I have hereunto set my hand this 18th day of April, 1929.

. JAMES L. MoFARLAND.

furnace substantially to its working temperature while filled with air, then admitting a non-explosive gas to purge the heated furnace of air and thereafter admitting hydro' gen to form the working medium.

3. The method of operating a brazing furnace which comprises heating said furnace to its' working temperature while filled with air, then admitting a non-explosive mixture of hydrogen and nitrogen to purge the heated furnace of air and thereafter admitting hydrogen in suflicient quantity to form a working medium.

4. The method of cooling a furnace where in a working medium explosive in character is used which comprises admitting a nonexplosive medium to the furnace in suflicient quantity to render the furnace gas non-explosive in character and thereafter opening said furnaceto the outside air. 

